<!doctype html>
<html lang="en">

<head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=1">
    <title>Color</title>
    <style>
        .box1 {
            width: 200px;
            height: 200px;
            background-color: black
        }

        .box2 {
            width: 100px;
            height: 100px;
            background-color: rgba(255, 255, 255, 0.5)
        }
    </style>
</head>

<body>
    <div class="box1">
        <div class="box2"></div>
    </div>
</body>

</html>